Manufacture of files



which is practically destroyed by the crystallisurface moreor lessdestroyed.

carbon in the absence of oxygen, whereby the Ma 23, 1882, No.'258,301 1have described carbon, thereby preserving the original granu- UNITEDSTATES MARTIN A. HOWELL, Ja,

PATENT OFFICE.

OF CHICAGO, ILLINOIS.

MANUFACTURE OF FILES.

SPECIFICATION forming part of Letters Patent No. 273,536, dated. March6, 1883.

- Application filed January 25, 1883. (No model.)

To all whom it may concern Be it known that I, MARTIN A. HOWELL, Jr., acitizen of the United States, residing at Chicago, Cook county,Illinois, have'invented new and useful Improvements in'the Manufactureof Files, of which the followingis a. specification.

My invention relates to certain improvements in the manufacture of filesfrom castiron blanks, in contradistinction from those files made fromforged blanks, whether the latter be steel or wrought-iron subsequentlyconverted into steel.

The object of my invention is to effect an improvement in themanufacture by casting the blanks, oxidizing thefree carbon therein, andthereby restoring the cohesion of the metal,

zation of the carbon, while the metal is et soft and at a high heat;surfacing and cutting said blanks while in this decarbonized state; and,finally, in the saturation of the out files with metal is restored toits carburized condition, atmospheric air or any traces of oxygen beingWholly excluded during the process of saturation and the subsequentcooling.

In the Letters Patent granted to me dated and claimed a process ofdeca'rburizing castiron blanks, surfacing and cutting the same While inthis condition, and subsequently recarburizing the finished files orrestoring the lar structure of the metal. By this process I avoid allforging, whereby the particles are crushed and the crystalline structureof the In practicing this process the generation of the vapors and gasesof hydrocarbon begins at a point far in advance of the tiinewhen therequired temperature of the enveloped metal isreached. As the heatincreases, the rapid generation and expansion of these vapors force anoutlet for escape, and by the time the metal is heated to the point ofsaturation the gases and vapors of hydrocarbon have become nearly wastedandintermingled with atmospheric air through leakage. Not only,therefore, is the process of saturation an imperfect one, but thepresence of the oxygen of the intermingled air causes a partialoxidation of the surface of the file,

thereby greatly injuring, if not ruining, it for vide flasks or chargerscapable of being hermetically sealed and of sufficient strength towithstand the required pressure. The cut files are placed in theseflasks, interlaid with or surrounded by materials which are rich inhydrocarbon-such, for example, as animal or vegetable carbon, petroleumand its products, resins, 850. The flask or flasks thus charged aresealed and connected, by means of a pipe or escape-tube, with a vesselfrom which the air has been previouslyexhausted. This vessel is placedin any suitable receptacle containing water and weighted to keep'itsubmerged. The shape and construction of this vessel is whollyimmaterial,s0 long as it answers the purpose of holding the gas whichflows into it from the flasks. The pipe connecting the flasks with thisvessel is furnished with a cock, for a purpose presently to bementioned. As the heat of the furnace advances, the vapors aregenerated, as already mentioned, long in advance :of the temperaturewhich is necessary to saturate the metal. The flasks containing thefiles also necessarily contain atmospheric air, and this air beingmingled with the first vapors generated, the

moisture is allowed to flow off through any suitable escape until thecurrent is free from traces of oxygen. The outlet is then closed, andthe cock in the escape-pipe is opened and the vapors allowed to flowinto the exhaustedvessel or gas-holder, where they are stored up for useat such time as the advancing heat shall have raised the tiles to thepoint of saturation, when the presence of said vapors will be requiredunder heavy pressure to the end of the. operation. By this means thevapors which under the former methods of carburization were dissipatedand lost are stored up and retained for use, and all danger of animperfect or partial saturation is avoided,

metal by the. oxidation of its surface through thepresence of air. Whenthe process is comas well as the further danger of injuring the I00plete and the files become saturated, the cock I in the escape-pipe isclosed and the flask is taken from the muffle or furnace and placed in apit, where it is covered with dry sand, lime, clay, or any suitablematerial which will preserve the heated flask from oxidation. Here it isallowed to cool down gradually, after which the contents are removed.The files being now charged with pure carbon, and no oxide beingpresent, they will withstand a much higher heat in hardening thanordinary steel, or any partially-oxidized metal. Therefore they arehardened in the usual manner without risk of oxidation, the result beingthe production of a tool showing all the characteristics of true carbon.'These files resist the abrasion of all ordinary metals to a degreeunsurpassed by any known product of steel.

It will be noticed that some of the steps of my process are old. Forexample, the decarbonization of iron and its subsequent recarbonizationhas been long known, and to thisI lay no claim. The essential feature ofthe process of manufacture I employ is in the exclusion of oxygen in thestage of reearburization and the storing of the hydrocarbon vapors underpressure until the point of saturation is reached.

The files produced by this process are castiron. This is evidenced bythe facts that the blanks are cast, (in contradistinction to beingforged,)whereby the granular structure of the metal is left unaltered.

By the process hereinbefore described the graphitic carbon of thefile-blanks (viz., the carbon crystallized between the particles ofmetal) is removed in order that the cohesion of the metal may berestored by running the blanks to a high heat. The entire decarburizingprocess is necessary to soften the blanks preparatory to cutting, torestore the cohesion of the metal and give a greater body for thesubsequent saturation with combined carbon. The metal treated in thismanner possesses manyofthe well-known characteristics ofwhite cast-iron.

It should be noted that one of the essential features of this inventionconsists in the removability of the flasks from the mufiie and theirgradual cooling while sealed to prevent the admission of air, the blanksnot being removed until they are cold, up to which time they aresurrounded by the vapors of hydrocarbon. The importance of this stepshould not be overlooked, as the presence. of small traces of oxygen,even when the metal is at a low red heat, would resultin oxidation. Whenthe flask is drawn it is immediately replaced by another, so that thecooling, charging, heating, &i:., may go on without delay.

In the present application I have described only the process ofmanufacture, the article produced thereby being claimedin an applicationfiled by me the 10th dayofNovember, 1882.

It will be noticed that the files are first cut and then carburized.They can be first carburized and then cut, which, in some cases, may bemore advantageous, but preferably I employ the former operation.

Having thus described my invention, what I claim is- In the manufactureof files, the deearburization, surfacing, and cuttingof the cast blanks,and their recarburization in a hermeticallyclosed flask from which allatmospheric air and traces of oxygen are sufi'ered to escape, the flaskbeing connected by a pipe with a vessel from which the air is exhausted,and in which the vapors of hydrocarbon are stored, under pressure, untilthe degree of temperature is reached at which saturation begins,thesealed flask being subsequently removed and allowed to cool before itis opened. whereby all danger of oxidation is avoided, substantially asdescribed.

In testimony whereof I have hereunto set my hand in the presence of twosubscribing witnesses. I

MARTIN A. HOWELL, JR.

Witnesses:

THOMAS H. HOWELL, JOHN W. HOWELL.

